Organic photovoltaic cells (OPVs) have received significant interest for their potential as a low-cost energy source and efficiencies have recently reached records nearing 10% using both solution and vacuum deposition methods. In the conventional orientation for organic photovoltaic cells, the OPV is illuminated through a transparent hole-collecting anode deposited on the substrate, (e.g. indium tin oxide (ITO)), and electrons are collected by a low work function metal cathode top contact. Development of efficient inverted device structures (e.g., wherein electrons are collected by a transparent cathode) (i) may provide more degrees of freedom in designing OPV fabrication schemes, including tandem and semitransparent devices, (ii) may allow for protection of the delicate organic semiconductor layers below metal oxide anode buffer layers prior to subsequent top layer deposition steps, and/or (iii) may have improved stable by allowing use of higher work function metal top contacts and/or protection of air-sensitive electron acceptor layer. However, due to the high work function of common transparent conductors (e.g. ITO and conductive polymers) such structures generally require a low work function interfacial cathode buffer layer, which aids in providing sufficient electric field through the device and/or may allow for ohmic contact with the adjacent electron acceptor.
Accordingly, improved cathode buffer materials and related devices and methods are needed.